1. Field of the Invention
The invention relates to an electronic headlight control circuit and more particulary relates to a circuit for turning on car lights in response to an external stimulus indicating that headlights are required and comprising a delay circuit for turning off headlights a predetermined period of time after the car's engine has been stopped.
2. Prior Art
From the prior art it is known that automotive headlights may be turned on by means of manual-operated switch or an automatic control. Similarly, a number of prior art devices are known for turning off headlights a predetermined period of time after the engine has been turned off. One prior art automatic headlight control circuit is disclosed in U.S. Pat. No. 3,769,519. The automatic control of that patent turns on automobile headlights by converting engine ignition pulses to a continuous level signal for activating a relay or the like. The control turns off the lights a predetermined period of time after the ignition impulses have ceased. A need for an inexpensive and reliable control circuit with a relative long time delay to cause the car's headlights to turn off a substantial period of time after the engine has been shut off, has been recognized. It is desirable to generate a time delay of several minutes to allow motorists to have the benefit of the headlights while leaving the automobile. The use of commonly known R-C circuits to achieve time delay is well known from the art. It is also known to those skilled in the art that a charged capacitor of nominal size discharges relatively rapidly and in order to obtain a time delay of more than a few seconds a physically large capacitor will be needed. The use of such capacitors has readily recognizable disadvantages. Apart from size disadvantages, larger capacitors which are commonly available have substantial leakage. Capacitor leakage is a particular problem where the capacitor is to be discharged over a long period of time.